Unsharp Mask

This applies a filter to the edges of a blurry colour variations eg around face and hair of a person.Apply an unsharp mask filter by:
Chose a copy of your picture in Menu options, click Filter - sharpen - Unsharp mask
Click on an edge of the picture eg edge of a face
Adjust sliders until you are happy with the image.
OK
To see the changes Click Window - History and a list of what you have done will be shown.